A high frequency magnetic field assisted magnetic recording head including a spin torque oscillator can generate a high frequency magnetic field by passing a drive current through the spin torque oscillator. The high frequency magnetic field generated by the head allows data to be recorded in a magnetic recording medium and has a larger anisotropy than a magnetic field generated by a conventional head.
In order to increase the intensity of the high frequency magnetic field, it is preferred to rotate a magnetization of an oscillation layer formed in the spin torque oscillator by a large angle by passing a large drive current through the spin torque oscillator. However, if an excessively large drive current is passed, the spin torque oscillator heats up due to the current flow (i.e., Joule heat), and the lifetime of the spin torque oscillator is shortened due to element diffusion inside the spin torque oscillator. Further, if such an extremely large drive current is passed, the spin torque oscillator may be instantly broken. Therefore, the drive current has to be controlled at or below a certain level so that the spin torque oscillator will not be broken. However, this level of current may not be large enough to increase the intensity of the high frequency magnetic field to a desired level.